Objective-C：如何覆盖/替换库中的类

I have to use a library "mylib.a" in my code, which source I cant access, though I know that there are some classes for e.g "NeededClass1", "NeededClass2". My problem is that I have also in my own code created classes with names "NeededClass1", "NeededClass2" and when I include both (the lib and my sources) I will get linking errors from the compiler. I have to use a library "mylib.a" in my code, w